The present invention relates to an organic EL element used as a planar light source or a display element, a method for manufacturing the same, and a display using the same.
Organic EL elements having a luminescent (light emitting) layer composed of an organic film, which can provide large-area, low-voltage display elements, are currently attracting a great deal of attention. Since an element structure having organic laminated layers of differing carrier transportation capabilities can be effectively used to improve the efficiency of such an element, an element has been proposed in which the positive-hole transfer layer and the luminous electron transportation layers comprise low-molecular aromatic amine and an aluminum chelate complex, respectively [C. W. Tang, Appl. Phys. Lett., 51, p. 913 (1987)]. With an applied voltage of 10 V or less, this element can provide high brightness of 1,000 cd/m2, which is sufficient for practical use.
At present, arbitrary organic dyes are used as a luminescence center (a light emitting center) to obtain arbitrary luminescent colors ranging from blue to red in the visible region. Furthermore, an RGB multicolor display (a display element) can be obtained by closely arranging picture elements having luminescent colors of red (R), green (G), and blue (B), which are the primary colors, in parallel on the same substrate.
However, in order to use a vacuum evaporation method to produce a multicolor display, particularly an RGB multicolor display with different luminescent colors as described above, picture elements with different luminescent colors must be sequentially produced on the same substrate using a shadow mask. Thus, compared to monochromatic luminescent picture elements, the above picture elements require a large amount of time and labor for production due to their small size, making them unsuitable for use in the manufacture of high-definition displays.
To solve these problems, Kido et al. have proposed an emitting element section that is adapted for white that is prepared in a contact print, but which can provide multiple colors by combining the element with a color filter, obviating an arrangement of EL elements over very small intervals or a preparation of elements having different luminescent colors [J. Kido, K. Nagai, Appl. Phys., Vol. 63, pp. 1026 to 1029 (1994)]. This method puts a color filter between a transparent substrate and a transparent electrode of material such as indium-tin oxide (ITO) in order to modulate emissions from an organic luminescent layer sandwiched between the ITO and a rear electrode.
A group at Idemitsu Kosan Co. has also proposed a combination of a blue-emitting element and a color-converting layer, in order to convert blue into green or red to arrange RGB picture elements (Nikkei Electronics, January, pp. 102, 1996). This method inserts a fluorescent color-converting layer between the ITO and the transparent substrate to convert blue light generated In the luminescent layer into green and red light.
Despite their simplicity, arrangements based on the color filter or blue color-converting methods are inefficient, due to photo-absorption losses resulting from the color filter or to conversion losses resulting from the color-converting layer.
This invention provides a solution to these problems, with the objective of creating an organic EL element that can provide high-luminous efficiency and is capable of easily providing multiple colors. The objectives also include a manufacturing method of such elements and the creation of a display incorporating such elements.
To attain said objects, an organic EL element according to this invention uses two or more types of organic dyes that can act as light emitting centers. In attempting to manufacture this element, we discovered that an organic light emitting dye layer may be partially irradiated with electromagnetic radiation (light) to modify one or more dye types through photo-oxidation or photolysis to keep the dyes from functioning fully as light emitting centers, or to change the colors of light emitted, thereby allowing the production of differing colors at irradiated and non-irradiated portions. The electromagnetic radiation used in this invention has a vacuum frequency of about 10xe2x88x9217 to 105 m and includes the xcex3-rays, X-rays, ultraviolet radiation, visible radiation, and infrared radiation and is in particular preferably ultraviolet radiation or visible radiation.
A first aspect of this invention involves a multicolor organic EL element, characterized in that the element includes a light emitting layer (a luminescent layer) containing at least two or more kinds of organic dyes acting as light emitting centers (luminescence centers) in which at least one of the organic element kinds is modified to change the colors of the light emitted by the element. The light emitting layer may consist of one or many layers.
A second aspect of this invention involves a method for manufacturing a multicolor organic EL element, involving the formation of a light emitting layer containing at least two kinds of organic dyes acting as light emitting centers, and the partial irradiation of the light emitting layer with electromagnetic radiation to modify at least one of these kinds of organic dye.
A third aspect of this invention involves a method for manufacturing a multicolor organic EL element having one or more light emitting layers containing organic elements acting as light emitting centers, characterized in that any light emitting layer is entirely or partially irradiated with electromagnetic radiation to modify at least one of these kinds of organic dye present within the irradiated area.
A fourth aspect of this invention involves a multicolor organic EL element, characterized in that in an organic electroluminescence element having a light emitting layer composed of at least one organic compound layer, the light emitting layer contains three or more kinds of organic dyes capable of acting as light emitting centers and emitting blue, green, and red light; and in that at least one of these kinds of organic dye is modified to change the color of the light emitted from the corresponding picture element.